The broad objective of this research was to develop a spatial model which provides both timely and quantitative regional maize yield estimates for real-time Early Warning Systems (EWS) by integrating satellite data with ground-based ancillary data. The Food and Agriculture Organization (FAO) Crop Specific Water Balance (CSWB) model was modified by using the real-time spatial data that include: dekad (ten-day) estimated rainfall (RFE) and Normalized Difference Vegetation Index (NDVI) composites derived from the METEOSAT and NOAA-AVHRR satellites, respectively; ground-based dekad potential evapo-transpiration (PET) data and seasonal estimated area-planted data provided by the Government of Kenya (GoK). A Geographical Information System (GIS) software was utilized to: drive the crop yield model; manage the spatial and temporal variability of the satellite images; interpolate between ground-based potential evapo-transpiration and rainfall measurements; and import ancillary data such as soil maps, administrative boundaries, etc. In addition, agro-ecological zones, length of growing season, and crop production functions, as defined by the FAO, were utilized to estimate quantitative maize yields. The GIS-based CSWB model was developed for three different resolutions: agro-ecological zone (AEZ) polygons; 7.6-kilometer pixels; and 1.1-kilometer pixels. The model was validated by comparing model production estimates from archived satellite and agro-meteorological data to historical district maize production reports from two Kenya government agencies, the Ministry of Agriculture (MoA) and the Department of Resource Surveys and Remote Sensing (DRSRS). For the AEZ analysis, comparison of model district maize production results and district maize production estimates from the MoA (1989-1997) and the DRSRS (1989-1993) revealed correlation coefficients of 0.94 and 0.93, respectively. The comparison for the 7.6-kilometer analysis showed correlation coefficients of 0.95 and 0.94, respectively. Comparison of results from the 1.1-kilometer model with district maize production data from the MoA (1993-1997) gave a correlation coefficient of 0.94. These results indicate the 7.6-kilometer pixel-by-pixel analysis is the most favorable method. Recommendations to improve the model are finer resolution images for area planted, soil moisture storage, and RFE maps; and measuring the actual length of growing season from a satellite-derived Growing Degree Day product.

Greenhouse and field experiments were conducted to determine how proximity factors and water stress interact to influence competition between purple nutsedge and upland cotton. Purple nutsedge produced more total dry weight than cotton in wet conditions but produced less or similar total dry weight in dry conditions. Cotton's ability to extract water from greater soil depth and maintain a high rate of photosynthesis during water stress enabled it to maintain higher RGR (relative growth rate), LAR (leaf area ratio), and leaf expansion than nutsedge. Absolute growth rate (AGR), initial propagule weight, and early shoot production were important parameters for purple nutsedge competition with cotton. Moisture stress affected the relative importance of intraspecific and interspecific competition between species in both greenhouse and field experiments. intraspecific competition was more important than interspecific competition in determining cotton biomass production in wet conditions but drier conditions further reduced the relative importance of interspecific competition. The results of all experiments indicate that greenhouse addition series competition experiments can be applicable to field conditions provided the experimental design takes into account the biological characteristics of the species being studied. Pot size had a large influence on intra- and interspecific competition between purple nutsedge and cotton. In greenhouse experiments, physiological measurements were initiated one hour after irrigation and repeated every 2 h throughout the day. One hour after the cessation of water stress, the photosynthetic rates of both species increased, but photosynthesis recovered faster in cotton than in purple nutsedge. The faster recovery of photosynthesis in cotton was probably due to the osmotic adjustment that occurred in cotton leaves that protected enzymes and other cellular components during water stress. In additive field experiments, seed cotton yield was reduced because the number of harvestable bolls m⁻¹ was reduced as purple nutsedge density increased. Yield was also reduced by cotton seedling death at the highest nutsedge density. The interference of purple nutsedge with cotton cannot be reduced through water management alone. But, based on the growth characteristics of indeterminate cotton varieties, we suggest that delaying the first post-planting irrigation of some cotton varieties could reduce the competition of purple nutsedge with cotton without affecting final seed cotton yield.

Aphis gossypii Glover (cotton-melon aphid) is a major pest of agriculture worldwide. Cucumis melo L. (melon) possesses monogenic resistance to this aphid, and is a good model for the study of aphid resistance mechanisms in plants. This dissertation presents analyses of the effects of the resistance gene on A. gossypii, and of the gene's effects on biochemical and molecular-genetic properties of melon plants. Nearly isogenic lines (NILs) of melon, either resistant or susceptible to A. gossypii, were compared for their influence on aphid life history traits and feeding behavior. The resistance trait delayed development, increased mortality, and markedly decreased reproduction of aphids confined to leaves of resistant plants. Aphids on resistant plants salivated into phloem sieve elements significantly longer, and were less likely to begin sap ingestion after salivation, suggesting that the resistance factor acts within phloem sieve elements. Biochemical properties of callose synthase were compared between NILs to test the hypothesis that callose deposition plays a role in the resistance mechanism. No differences were detected between resistant and susceptible melon genotypes with respect to callose synthase subunit abundance or in vitro enzyme activity. Sixty-four F₃ families from a melon mapping population were tested for aphid resistance to place the resistance locus on a genetic map of the melon genome. Four molecular markers were found to be linked to the aphid resistance phenotype. The name Agr ( Aphis gossypii resistance) is proposed for this locus. The closest flanking markers were positioned at 4.3 and 7.0 cM from Agr. Evidence suggests Agr might be a member of the nucleotide binding site-leucine-rich repeat (NBS-LRR) family of plant resistance genes, which are known to cluster in plant genomes. Melon genomic DNA sequences homologous to this gene family were isolated to test the hypothesis that Agr is an NBS-LRR homolog. Two of these sequences were tested for genetic linkage to Agr in a population of F₂ plants segregating for the resistance trait. DNA gel blot analysis determined that one sequence, NBS-2, is approximately 2.7 cM distant from Agr, which suggests Agr resides in a cluster of NBS-LRR homologs and could be a member of this gene family.

In the mid-1980s, a new biotype of Bemisia tabaci was introduced into the southern U.S. causing extensive damage to agricultural crops throughout the region. An augmentative biological control project was initiated using a native parasitoid, Eretmocerus eremicus to determine its efficacy against B. tabaci infesting cotton in the desert areas of California and Arizona. A series of experiments were conducted in 1992-1995: release rate studies in cages and open fields; parasitoid dispersal within fields to determine movement rates after point release; and experiments to determine the parasitoid-host spatial relationship. Cage release rate studies, demonstrated that rates of parasitism could be increased 61 to 79% in the highest release treatments, with reductions in whitefly densities of 80 to 100% relative to control treatments. Cotton yields in the high release treatments peaked at 2.5 bales/ac and were 2.6 to 4.2 times greater than in control treatments. Effective release rates were estimated to be equivalent to 770,000 to 1.1 million parasitoids/ha. Field releases equivalent to 7.9 million parasitoids/ha resulted in a peak rate of parasitism of 42% but there were no statistical differences in parasitism, whitefly densities, or cotton yield; relative to no-release plots. High levels of whitefly immigration from surrounding crops, and parasitoid dispersal from release plots, diluted the effects of release. In a second field release rate study, releases equivalent to 2.0 to 3.0 million parasitoids/ha increased levels of the percentage of discovered leaves to greater than 80%. Parasitoid dispersal was analyzed with mark-recapture experiments and data were fit to a diffusion model. One female wasp flew 82 m in one day though the majority of wasps flew a few meters or less. Estimated diffusion rates and median dispersal distances were 0.40 to 0.71 m²/min and 2.4 to 4.4 m/(4 to 8) days respectively. Analysis of dispersal data suggested that releases on 20 m centers would provide effective coverage within a field. Density independent parasitism was common at the spatial scale of leaves and plants. There was positive density dependence for the percentage of discovered leaves suggesting that parasitoids aggregate to high density patches of whitefly but fail to achieve high levels of parasitization possibly due to egg limitation or mutual interference.

Heliolithine moth larvae are serious agricultural pests causing hundreds of millions of dollars in agricultural damage annually. Mating disruption, a behavioral method of control of adult male sexual response to female pheromones, has been successfully administered in the field for many years, yet the underlying mechanisms that account for mating disruption are poorly understood. Habituation, a form of nonassociative learning, has been implicated as one possible mechanism that effects male moth behavior during the application of mating disruption strategies. To substantiate the claim that habituation can play a role in mating disruption, data were collected on five of habituation's classic characteristics: (1) The existence of a negatively accelerated relationship between trials and response strength; (2) Spontaneous recovery of response strength; (3) A long-term reduction in male moth pheromonal response strength; (4) More rapid reduction of response strength and greater spontaneous recovery of response with less intense stimuli; (5) Learning associated with a highly specific stimuli will not generalize to exceedingly dissimilar stimuli. Results of this study clearly indicate that all five characteristics related to habituation were present. Specifically, males, repeatedly exposed to pheromones of conspecifics, display a decrease in response strength. Response reduction and spontaneous recovery were both found to be greater with less complex stimuli. Long-term habituation was successfully demonstrated for up to 96 hours post habituation training. Most importantly, it was found that males, habituated to one blend, demonstrated little habituation when exposed to a second blend. Additionally, it was found that a substantial amount of individual differences in responsiveness to habituation training exists between males of this species. The findings of this study indicate two major points. First, habituation can be used as part of an effective integrated pest control strategy. However, because there is a substantial amount of individual differences in habituation susceptibility, some male moths may experience greater reproductive success. Further, because the males did not generalize habituation across the two stimuli presented in this study, there is concern that if all known pheromone components of this species are not used in field applications, males will habituate to the applied pheromone but not individual females.

Quality Protein Maize (QPM) genotypes are opaque2 (o2) mutants that, through the action of modifier genes, develop a hard, vitreous endosperm. QPM kernels have the increased level of lysine observed in o2 mutants, but the appearance and physical properties of normal genotypes. In this dissertation, two important aspects regarding the development of QPM genotypes are addressed: the process of o2 endosperm modification and the accumulation of lysine in the endosperm. The formation of vitreous endosperm in o2 kernels is associated with the increased accumulation of the 27-kD γ-zein protein. When modifier genes were backcrossed into a normal (non-o2) genotype, higher levels of γ-zein were observed in the endosperm, similar to what happens with o2 mutants. However, in this case the increase in γ-zein content did not translate into increased endosperm hardness or density. Thus, there appear to be limits in the extent to which γ-zein can affect the physical properties of the endosperm. It has been suggested that the AB allele of the γ-zein locus is necessary, but not sufficient, for o2 endosperm modification. However, a recombinant o2 plant homozygous for the γ-zein rA allele was identified, in which the kernels have a uniformly vitreous endosperm and increased level of γ-zein protein. This indicates that the formation of vitreous endosperm in o2 genotypes does not require the presence of the AB γ-zein allele and that the increased level of γ-zein protein in modified o2 endosperm is not dependent on the presence of two γ-zein coding sequences. Very little is known about the proteins that account for the majority of lysine in maize endosperm. A close relationship between the level of non-zein proteins and endosperm lysine content was determined. Additionally, a very high correlation between the concentration of the protein synthesis factor, EF-1α, and the lysine content of the endosperm was found. This is a significant step towards understanding the biochemical basis of lysine accumulation in the endosperm. EF-1α content can be used as an indicator of lysine levels for breeding programs, as well as a tool to investigate factors influencing the accumulation of lysine-rich protein in maize endosperm.

Little is known about the crown system and its association with plant growth and development in spring cereals. This study investigated temperature, seeding depth and genotypic effects on crown development of barley; relationships between crown and seminal root systems; and classification and description of crown systems under deep seeding. Two greenhouse experiments were performed using PVC tubes. Low temperature and deep seeding reduced percentage and rate of emergence but increased crown number, crown depth, and crown weight in most genotypes. Crown number, crown depth and crown weight showed increased associations with seminal root, whole root, and shoot weight at low temperature and deep seeding in most genotypes. Deep plantings showed that crown systems of barley can be classified as unicrown, bicrown and multicrown types with some variants. One line produced plants with no subcrown internode under 12.5 cm planting. Our results suggested that the crown is a potential source of crown roots and tillers.

Previous variability studies in both U.S. and worldwide agriculture have indicated that crop production has been accompanied by increasing variation. In this research, four different variability indexes were estimated in order to evaluate the production variability associated with the major Arizona field crops. Results show that major Arizona field crops, which are all irrigated, did not have a uniform production variability over the last 24 years and the variability of these crops did not generally increase between the periods of 1967-1978 and 1979-1990. Although biological factors (e.g. pests, weather) influenced variability, the variation of crop production measures over time also was related to market factors (e.g. prices), government farm programs, producers' crop management experience, and the geographical area selected for the analysis. Crops covered by government farm programs usually varied more in harvested acreage and fluctuated less in yield per acre than vegetable crops.

<p> The Runoff Risk Advisory Forecast (RRAF) provides Wisconsin's farmers with an innovative decision support tool which communicates the threat of undesirable conditions for manure and nutrient spreading for up to 10 days in advance. The RRAF is a pioneering example of applying the National Weather Service's hydrologic forecasting abilities towards the Nation's water quality challenges. Relying on the North Central River Forecast Center's (NCRFC) operational Snow17 and Sacramento Soil Moisture Accounting Models, runoff risk is predicted for 216 modeled watersheds in Wisconsin. The RRAF is the first-of-its-kind real-time forecast tool to incorporate 5-days of future precipitation as well as 10-days of forecast temperatures to generate runoff risk guidance. The forecast product is updated three times daily and hosted on the Wisconsin Department of Agriculture, Trade, and Consumer Protection (DATCP) website. Developed with inter-agency collaboration, the RRAF model was validated against both edge-of-field observed runoff as well as small USGS gauged basin response. This analysis indicated promising results with a Bias Score of 0.93 and a False Alarm Ratio (FAR) of only 0.34 after applying a threshold method. Although the threshold process did dampen the Probability of Detection (POD) from 0.71 to 0.53, it was found that the magnitude of the events categorized as hits was 10-times larger than those classified as misses. The encouraging results from this first generation tool are aiding State of Wisconsin officials in increasing awareness of risky runoff conditions to help minimize contaminated agriculture runoff from entering the State's water bodies.</p>

<p> The rice stink bug, <i>Oebalus pugnax</i>(F.), is an important late season pest of rice that is noted for causing grain yield and quality reductions in the United States. This study investigated rice injury using field cages in two rice cultivars ('Cocodrie' and 'Wells') at bloom, milk, and soft dough stages and <i>O. pugnax</i> ecology in the Delta Region of Mississippi. </p><p> Specific objectives were: 1) to determine the impact of adult <i> O. pugnax</i> infestation on rice yield and grain quality at bloom, milk, and soft dough stages of rice development; 2) to determine the impact of adult <i> O. pugnax</i> gender and infestation duration on rice yield and grain quality at the milk stage of panicle development; 3) to identify and examine the seasonal abundance and phenology of <i>O. pugnax</i>on non-cultivated host grasses; and 4) to evaluate feeding preference and development of <i> O. pugnax</i> on host grasses. </p><p> Rice injury increased as <i>O. pugnax</i> density increased. The bloom and milk stages were the most vulnerable to blank and discolored kernels, respectively. <i>O. pugnax</i> feeding injury was significant after 3 d of infestation duration during the milk stage of panicle development. Female <i>O. pugnax</i> caused a greater percentage of blank kernels compared to males. </p><p> A survey of <i>O. pugnax</i> hosts indicated that Italian ryegrass, <i> Lolium perenne</i> L. ssp. <i>multiflorum</i> and winter wheat, <i> Triticum aestivum</i> L., were important hosts during spring and early summer. Junglerice, <i>Echinochloa colona</i> (L.) Link; crabgrass spp., <i>Digitaria</i> spp. Haller; southwestern cupgrass, <i> Eriochloa acuminata</i> (J. Presl) Kunth; and praire cupgrass, <i> Eriochloa contracta</i> (Hitchc.), were important hosts for <i> O. pugnax</i> during early to mid-summer. Browntop millet, <i>Urochloa ramosa</i>, and broadleaf signalgrass, <i>Urochloa platyphylla</i>, supported adult <i>O. pugnax</i> prior to overwintering. In a choice test of wild host grasses, junglerice was the most preferred over 10 other host grasses. In the no-choice test, mean development time was shorter and survival was greater for <i>O. pugnax</i> nymphs reared on rice, <i> Oryza sativa</i> L., compared to dallisgrass, <i>Paspalum dilatatum </i> Poir and junglerice. These results provide biological and ecological information on which new <i>O. pugnax</i> integrated pest management practices can be developed.</p>